Mineralogical composition and spatial variation of ... · The present study investigates the...

International Research Journal

Vol. 6(11), 16-22, November (2017)

International Science Community Association

Mineralogical composition

2nd

order channel of the Brahmaputra River in Majuli, Assam, IndiaSuman Saikia

Department of Geological Sciences, Gauhati University, Guwahati, Assam, India

AvailableReceived 28th August

Abstract

The Brahmaputra River flows across Assam in a braided pattern with large discharge and heavy sediment load. The present

study investigates the post-monsoon mineralogical variations in the suspended load in a 2

Brahmaputra River in Majuli, Assam. The channel flows along the southern bank of Majuli. Representative suspended

sediment samples were collected from different locat

subjected to laboratory analysis for the determination of amount of suspended load as well as their mineralogical content.

The suspended load varies from 0.337 gm/l to 1.77 gm/l. X

quartz, chlorite, chamosite, strontianite, sanidine, orthoclase, tourmaline, albite, oligoclase, augite, hornblende, biotite,

muscovite, enstatite, epidote calcite, dolomite, hematite, goethite,

kyanite, rutile, zoisite, clinozoisite and glauconite. The clay minerals varieties found are illite, montmorillonite and chlo

A decrease in the amount of suspended load is observed from upstre

drop in stream power and change in flow direction of the 2

of minerals is observed along the course of the river channel.

Keywords: Brahmaputra River, Sedimentation, Suspended sediment, Mineralogy.

Introduction

Large Rivers constitute the main pathways of solutes and

suspended particles from the continents to the oceans

the study of sediment load carried by rivers and canals has been

the subject of intensive research for centuries, due to its

importance in the regulation of river and canal systems

studies also greatly assist in study of sediment characteristics for

example sediment types, nature of movement, amount of

sediment present and to solve various problems related to

sedimentation.

The Brahmaputra river of South Asia is the fourth largest river

in the world in terms of annual discharge

discharge is approximately 20,000m3/s

4 and has an average

annual sediment load of about 735 million metric tonnes

Assam, the river displays a braided pattern with large discharge

and heavy sediment load and active lateral migration

conspicuous feature of the Brahmaputra River is the presence of

large alluvial islands of which several are more than a century

old and inhabited as well7. One such island is Majuli, which is

located in the upper reach of the Brahmaputra valley in the

Majuli District of Assam. This island has been recognized as the

largest riverine island in the world. It has a population of 0.16

million people and is the seat of many Vaishnavite spiritual

center’s called ‘Satras’7.

The present study investigates the post-monsoon mineralogi

variations in the suspended load in a 2nd

order channel of the

Journal of Environmental Sciences___________________________

(2017) I

Association

composition and spatial variation of suspended sediments in a

order channel of the Brahmaputra River in Majuli, Assam, IndiaSuman Saikia

* and Jayanta Jivan Laskar

Department of Geological Sciences, Gauhati University, Guwahati, Assam, India

[email protected]

Available online at: www.isca.in, www.isca.me August 2017, revised 9th November 2017, accepted 20th November 201


monsoon mineralogical variations in the suspended load in a 2


sediment samples were collected from different locations and depths along the 2nd

order channel, which were subsequently


The suspended load varies from 0.337 gm/l to 1.77 gm/l. X-ray Diffraction analysis of the sediments indicate the presence of


muscovite, enstatite, epidote calcite, dolomite, hematite, goethite, gypsum, garnet, apatite, tourmaline, zircon, silimanite,

kyanite, rutile, zoisite, clinozoisite and glauconite. The clay minerals varieties found are illite, montmorillonite and chlo

A decrease in the amount of suspended load is observed from upstream towards the downstream part of the channel due to

drop in stream power and change in flow direction of the 2nd

order channel in its downstream portion. No clear segregation

of minerals is observed along the course of the river channel.

Brahmaputra River, Sedimentation, Suspended sediment, Mineralogy.

Large Rivers constitute the main pathways of solutes and

suspended particles from the continents to the oceans1. As such,

study of sediment load carried by rivers and canals has been

the subject of intensive research for centuries, due to its

importance in the regulation of river and canal systems2. These

studies also greatly assist in study of sediment characteristics for

ample sediment types, nature of movement, amount of

sediment present and to solve various problems related to

The Brahmaputra river of South Asia is the fourth largest river

in the world in terms of annual discharge3. The average

and has an average

annual sediment load of about 735 million metric tonnes5. In

Assam, the river displays a braided pattern with large discharge

and heavy sediment load and active lateral migration6. Another

of the Brahmaputra River is the presence of

large alluvial islands of which several are more than a century

. One such island is Majuli, which is

located in the upper reach of the Brahmaputra valley in the

am. This island has been recognized as the

largest riverine island in the world. It has a population of 0.16

million people and is the seat of many Vaishnavite spiritual

monsoon mineralogical


Brahmaputra River which flows along the southern bank of

Majuli in the Majuli District of Assam. This portion of the area

is not affected by sediment supply from any other source except

the Brahmaputra River.

Location of the study area: The study area is situated in the

southern part of Majuli between latitude 26°54’18.19’’ and

26°57’56.42’’N and longitude 94°08’47.56’’ and 94°17’26.14’’

E (Figure-1). The approximate length of the channel is 13 km.

Methodology

Field investigations in the river channel were carried out

immediately after the recession of floods with the help of a

mechanized boat. During the course of field investigation,

representative suspended-load samples were collected from

different locations and depths by means of a customized

suspended sample sampler of capacity 1 litre. T

coordinates were recorded with the help of a hand

receiver (Garmin e-Trex). The water+sediment samples were

carefully collected in labeled polypropylene bottles for

laboratory analysis.

In the laboratory, the collected water + sedimen

left undisturbed and allowed to settle down for one week. At the

end of a week, the overlying water from the settling vessels

containing the sediment + water mixture was carefully decanted

off, without allowing any of the contained sediments

off with the water. The remaining portion of the sediment +

________________________________ ISSN 2319–1414

Int. Res. J. Environmental Sci.

16

spatial variation of suspended sediments in a

order channel of the Brahmaputra River in Majuli, Assam, India

2017


monsoon mineralogical variations in the suspended load in a 2nd



order channel, which were subsequently


iffraction analysis of the sediments indicate the presence of


gypsum, garnet, apatite, tourmaline, zircon, silimanite,

kyanite, rutile, zoisite, clinozoisite and glauconite. The clay minerals varieties found are illite, montmorillonite and chlorite.

am towards the downstream part of the channel due to

order channel in its downstream portion. No clear segregation

Brahmaputra River which flows along the southern bank of

Majuli in the Majuli District of Assam. This portion of the area

is not affected by sediment supply from any other source except

: The study area is situated in the

between latitude 26°54’18.19’’ and

26°57’56.42’’N and longitude 94°08’47.56’’ and 94°17’26.14’’

1). The approximate length of the channel is 13 km.

Field investigations in the river channel were carried out

ession of floods with the help of a

mechanized boat. During the course of field investigation,

load samples were collected from

different locations and depths by means of a customized

suspended sample sampler of capacity 1 litre. The location

coordinates were recorded with the help of a hand-held GPS

Trex). The water+sediment samples were

carefully collected in labeled polypropylene bottles for

In the laboratory, the collected water + sediment samples was

left undisturbed and allowed to settle down for one week. At the

end of a week, the overlying water from the settling vessels

containing the sediment + water mixture was carefully decanted

off, without allowing any of the contained sediments to drain

off with the water. The remaining portion of the sediment +

International Research Journal of Environmental Sciences ____________________________________________ISSN 2319–1414

Vol. 6(11), 16-22, November (2017) Int. Res. J. Environmental Sci.

International Science Community Association 17

water mixture was subsequently passed through a filter paper to

separate the remaining portion of water from the sediments. The

suspended sediments in the filter paper is oven dried at 80oC for

24 hour, weight of each sample was measured and stored in air-

tight plastic bags for further laboratory investigations.

The next step involved the preparation of oriented slide mounts

of the sediments for XRD (X-Ray Diffraction) analysis. This

was accomplished by mixing a small portion of the sediments

with distilled water on an oriented glass slide and allowing them

to settle by gravity and dry under room temperature. The

resulting mixture after almost 24 hours formed a thin and

uniform coating on the slide once the water evaporates off.

The mineralogical composition of the suspended sediments was

determined by X ray diffraction analysis on a Rigaku TTRAX-

III X-ray Diffractometer at the Indian Institute of Technology,

Guwahati. The operational parameters of the system was set as

follows:

Instrument Operating Voltage – 9 KW, Cuk alpha radiation (θ =

1.54Ao), and 2 θ: 2 to 40

o

Diffraction occurs for each angle of incidence which satisfies

Bragg’s equation which states nλ= 2dsin θ, where n is a whole

number, λ= the X-ray wavelength, d = the distance between

planes of atoms and θ is the angle of incidence. The various

constituent minerals were identified from calculated 2θ and ‘d’

values and the relative intensities from standard ASTM Powder

Diffraction Data File8. Clay minerals were identified from

standard chart for oriented sample9.

Results and discussion

Table-1 shows the amount of suspended sediment (in gm.) per

liter of water, at various locations of the study area.

Table-1: Table showing weight of suspended sediment at

various locations.

Sampling location Weight(gm.)

1 0.44746

2 1.123656

3 0.42665

4 0.55001

5 1.76578

6 1.18672

7 0.45584

8 0.36956

9 0.39722

10 0.36649

11 0.62668

12 0.33665

13 0.61518

14 1.055

The total suspended load at various location ranges between

0.337 gm/l and 1.77 gm/l. The spatial variation of suspended

load along the river channel is shown in Figure-2.




Figure-1: Location map of the study area.

Figure-2: (a) Sampling location point marked on the map, (b) Graph showing spatial variation of suspended sediment load at

different locations in the study area.

The graphical plot of amount of suspended sediment at various

locations indicates greater amount of suspended sediment load

(up to location 6) in the upstream part of the channel. The

suspended load decreases downstream beyond sample location

no.6. This might be caused due to loss of stream power because

of change in the course of the river channel around this location.

Further beyond, the suspended sediment load again shows an

increasing trend near the confluence of the 2nd

order channel

with the main channel of the Brahmaputra River.

The x-ray diffractograms of oriented suspended load were

examined to identify their mineralogical content (Figure-3). The

various parameters determined during the study were 2θ, “d”

spacing and relative intensity.

123456789101112131415

Wt

(gm/lit)

Downstream Sampling location point Upstream

b




Figure-3: X-Ray Diffractograms of suspended sediment samples.

The most frequent and prominent peaks in the diffractograms

are shown by quartz, illite and montmorillonite. Chlorite,

Chamosite, Strontianite, Sanidine, Orthoclase, Tourmaline also

show prominent peaks in some samples. Quartz is identified by

a prominent peak at 26.66° 2θ, 3.343 A° d value and relative

intensity of 100. Montmorillonite shows peaks between 5.89°

and 6.80° 2θ. Illite shows peaks at approximately 8.8°, 17.7°

and 26.75° 2θ. Chlorite shows peaks at approximately 6.3° 2θ.

Chamosite shows reflection at 12.56° 2θ and 7.05A° d value.

Orthoclase peak occurs at 28.06° 2θ, 3.18 A° d value and a

relative intensity of 42. Strontianite shows 36.60° 2θ, 2.45 A° d

value and a relative intensity of 40. Besides these minerals,

minor peaks observed in the diffractograms indicate the

presence of Albite, Oligoclase, Augite, Hornblende, Biotite,

Muscovite, Enstatite, Epidote Calcite, Dolomite, Hematite,

Goethite, Gypsum, Garnet, Apatite, Tourmaline, Zircon,

Silimanite, Kyanite, Rutile, Zoisite, Clinozoisite and

Glauconite. The clay mineral varieties found are Illite,

Montmorillonite and Chlorite.

The spatial distribution of mineralogical assemblage found at

various sampling locations is shown in Table-2 and Figure-4.

Figure-4 depicts the spatial variation of the mineral assemblage

along the course of the river.




Table-2: Tabulated data of mineralogical composition of various analyzed suspended load sediments.

Sam

ple

no

Alb

ite

An

acli

me

Ap

atit

e

Au

git

e

Bio

tite

Cal

cite

Ch

amo

site

Ch

lori

te

Cli

no

zois

ite

Do

lom

ite

En

stat

ite

Ep

ido

te

Hem

atit

e

Gar

net

Go

eth

ite

Gla

uco

nit

e

Ho

rnb

lend

e

Illi

te

Illm

enit

e

Ky

anit

e

Mo

ntm

ori

llo

nit

e

Mu

sco

vit

e

Oig

ocl

ase

Ort

ho

clas

e

Qu

artz

Ru

tile

San

idin

e

Sil

lim

anit

e

Sp

hen

e

Sta

uro

lite

Str

on

tian

ite

To

urm

alin

e

Tre

mo

lite

Zir

con

Zo

isit

e

1 ● ●

● ● ● ● ●

● ●

● ●

●

● ●

2 ● ●

● ●

●

● ● ● ● ● ●

●

●

●

●

3

●

● ●

●

●

● ●

● ●

●

4 ●

●

●

●

●

● ●

●

●

●

5 ●

●

●

●

●

● ●

●

●

6 ●

●

●

●

● ● ● ●

● ●

7

● ●

●

●

●

● ●

●

●

● ●

8 ●

●

●

●

● ●

●

●

●

9 ●

●

●

●

● ●

● ●

●

●

●

10

●

● ●

●

●

●

●

● ●

●

11 ●

● ●

●

●

● ●

●

12 ●

● ●

● ●

●

● ●

● ●

●

13 ●

● ● ●

●

● ● ● ● ● ● ●

● ●

14 ●

●

●

●

●

● ●

●

●

Figure-4: Schematic diagram of the study area showing sample location (black dot) and the associated mineral assemblage.




Table-2 and Figure-4 indicate that there is no distinct indication

of lateral segregation of various mineral fractions in the

suspended load along the course of the river channel. Quartz,

albite, illite, montmorillonite, chlorite, strontianite show

consistent occurrence in all locations. Hornblende, garnet and

kyanite occur only in upstream portion of the study area,

whereas hematite, rutile, sillimanite and calcite are restricted to

the downstream portion.

Conclusion

The study reveals that the suspended load in the 2nd

order

channel of the Brahmaputra river near Majuli ranges between

0.337 gm/l to 1.77 gm/l. The suspended load is high in the

upstream portion of the channel, and decreases in the

downstream portion. This is probably due to drop in the stream

power due to change in the flow direction of the 2nd

order

channel in its downstream portion.

XRD analysis of suspended sediment indicate that the

suspended sediment contain quartz, chamosite, strontianite,

sanidine, orthoclase and tourmaline. Other minerals identified in

the x-ray diffractograms are albite, oligoclase, augite,

hornblende, biotite, muscovite, enstatite, epidote calcite,

dolomite, hematite, goethite, gypsum, garnet, apatite,

tourmaline, zircon, silimanite, kyanite, rutile, zoisite,

clinozoisite and glauconite. The clay minerals present are illite,

montmorillonite and chlorite. No systematic variation in the

mineral distribution could be identified along the course of the

river channel.

Acknowledgement

The authors thank the Head, Department of Geological

Sciences, Gauhati University for the laboratory facilities. One of

the authors (SS) would like to thank the University Grants

Commission, New Delhi, for providing the necessary research

fellowship under National Fellowship for Students of Other

Backward Classes Programme. The authors would also like to

thank Dr. S. Sarma, of Department of Physics, IIT Guwahati for

providing the laboratory facilities for XRD analysis of the

sediments. The equipment has been procured under DST FIST

Grant SR/FST/PSII-020/2009 (Physics). A special thanks also

goes to all who helped us during field-work and collection of

suspended sediment.

References

1. Campodonico V.A., García M.G. and Pasquini A.I. (2016).

The geochemical signature of suspended sediments in the

Parana River basin: Implications for provenance,

weathering and sedimentary recycling. Catena, 143, 201-

214.

2. Acharya Anu (2011). Experimental study and numerical

simulation of flow and sediment transport around a series of

spur dikes. Dissertation thesis. The University Of Arizona

UMI Number: 3454308, 192.

3. Mahanta C., Zaman A.M., Newaz S.M.S., Rahman

S.M.M., Mazumdar T.K., Choudhury R., Borah P.J. and

Saikia L. (2014). Physical Assessment of the Brahmaputra

River Ecosystems for Life: A Bangladesh-India Initiative,

Dialogue for Sustainable Management of Trans Boundary

Water Regimes in South Asia. Ch- 2, IUCN 2014, 90.

4. Immerzeel W. (2008). Historical trends and future

predictions of climate variability in the Brahmaputra basin.

International Journal of Climatology, 28(2), 243-254.

5. Datta B. and Sing V.P. (2004). Hydrology. The

Brahmaputra Basin Water Resources, Singh V.P., Sharma

N., Shekhar C. and Ojha P., Kluwer Academic Publishers,

Netherlands, 139-195.

6. Coleman J.M. (1969). Brahmaputra river channel processes

and sedimentation. Sedimentary Geology, 3(2), 129-239.

7. Lahiri S.K. and Sinha R. (2014). Morphotectonic evolution

of the Majuli Island in the Brahmaputra valley of Assam,

India inferred from geomorphic and geophysical analysis.

Geomorphology, 227, 101-111.

8. Lindholm Roy C. (1987). A Practical Approach to

Sedimentology. Allen and Unwin, Inc, USA., 276.

9. Carroll D. (1970). Clay Minerals: A guide to their x-ray

identification. Geol. Society of America, Boulder, Colorado.

Spl., 126, 80.

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